Reducing agents for use in thermographic recording materials

Abstract

A substantially light-insensitive black and white monosheet thermographic recording material is provided comprising a support and a thermosensitive element containing a substantially light-insensitive organic silver salt, a 1,2-dihydroxyphenyl-compound in thermal working relationship therewith and a binder, wherein the 1,2-dihydroxyphenyl-compound is represented by formula (I): where R is -P(=O)R1R2, -SOxR3, -CN, -NO2 or -CR4=NR5 when n is 0; R is -P(=O)R1R2, -SOxR3, -CN, -NO2, -CR4=NR5 or -COR6 when n is an integer; R1 and R2 are independently an alkyl, an aryl, an alkoxy, an aryloxy, a hydroxy or an amino group; R3 is an alkyl, an aryl or an amino group; R4 is an alkyl or an aryl group or hydrogen; R5 is an alkyl, an aryl, a hydroxy, an alkoxy, an aryloxy, an acyl or an amino amino group; R6 is an alkyl, an aryl, an alkoxy, an aryloxy, a hydroxy or an amino group or hydrogen; x is 1, 2 or 3; and the benzene ring of the 1,2-dihydroxyphenyl-compound represented by the formula (I) may be further substituted.

Description

The present invention relates to black and white substantially light-insensitive thermographic recording materials comprising a thermosensitive element containing a substantially light-insensitive organic silver salt and a novel reducing agent.Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy. In thermography three approaches are known:1. Direct thermal formation of a visible image pattern by image-wise heating of a recording material containing matter that by chemical or physical process changes colour or optical density.2. Image-wise transfer of an ingredient necessary for the chemical or physical process bringing about changes in colour or optical density to a receptor element.3. Thermal dye transfer printing wherein a visible image pastern is formed by transfer of a coloured species from an image-wise heated donor element onto a receptor element.Most of the "direct" thermographic recording materials are of the chemic...

AI Technical Summary

Benefits of technology

It is therefore an object of the present invention to provide thermographic recording materials whose prints have high D.sub.max and low D.sub.min levels and exhibit improved archivability and / or improved light stability and / or improved colour neutrality over the whole range of print densities.

The above mentioned binders or mixtures thereof may be used in conjunction with waxes or "heat solvents" also called "thermal solvents" or "thermosolvents" improving the reaction speed of the redox-reaction at elevated temperature. By the term "heat solvent" in this invention is meant a non-hydrolyzable organic material which is in a solid state in the recording layer at temperatures below 50.degree. C., but becomes a plasticizer for the recording layer where thermally heated and / or a liquid solvent for at least one of the redox-reactants.

In order to obtain improved shelf-life and reduced fogging, stabilizers and antifoggants may be incorporated into the thermographic recording materials of the present invention.

In a preferred embodiment of the present invention a protective layer is provided for the thermosensitive element. In general this protects the thermosensitive element from atmospheric humidity and from surface damage by scratching etc. and prevents direct con-act of printheads or heat sources with the recording layers. Protective layers for thermosensitive elements which come into contact with and have to be transported past a heat source under pressure, have to exhibit resistance to local deformation and good slipping characteristics during transport past the heat source during heating.

Problems solved by technology

However, prints produced with direct thermal recording materials using reducing agents according to the teaching of U.S. Pat. No. 5,582,953 exhibit unsatisfactory archivability, insufficient light stability over the whole sensitometric range and unsatisfactory colour neutrality.